[Python-ideas] namedtuple from ordereddict

[Serhiy Storchaka]

20.07.17 23:17, Jim J. Jewett пише:
> Several of the replies seemed to suggest that re-using the current
> dict structure for a tuple wouldn't work.  Since I'm not sure whether
> people are still thinking of the old structure, or I'm missing
> something obvious, I'll be more explicit.
> 
> Per https://github.com/python/cpython/blob/master/Include/dictobject.h#L40
> the last element of a dict object is now a separate pointer to
> ma_values, which is an array of objects.
> 
> Per https://github.com/python/cpython/blob/master/Include/tupleobject.h#L27
> the last element of a tuple object is also an array of objects.
> 
> Is there some reason these arrays cannot be the same memory?  e.g.,
> does a tuple header *have* to be contiguous with its data, and if so,
> is there a reason that the dict's ma_array can't be allocated with an
> extra tuple-header prefix?

Having a tuple header to be contiguous with its data decreases a total 
size of consumed memory, decreases memory fragmentation, speeds up 
tuple's creation and item access. Memory consumption and performance of 
tuples are critically important.

Allocating the dict's ma_values with an extra tuple-header prefix will 
increase memory consumption for instance dictionaries and will 
complicate the dict implementation (this can harm the performance). This 
also will increase a code coupling between dicts and tuples.

Named tuples are rarely used in comparision with ordinary tuples and 
dictionaries, and they shouldn't be improved at the cost of tuples and 
dicts.